Orthodontics focuses on diagnosis, planning, and treatment of various types of dental and skeletal malocclusions, for the purpose of improving the position and movement of the teeth. Orthodontic procedures, for example, readjust the position of teeth so that the teeth function optimally and are more aesthetically pleasing. Various types of appliances such as braces and wires can be positioned on a patient's teeth by a practitioner such as an orthodontist or a suitably trained dentist. Once mounted on the teeth, the hardware exerts continual forces on the teeth and gradually urges the teeth toward their ideal positions. Over a period of time, the practitioner adjusts the braces and the wires to urge the teeth toward their final destination.
Dental study casts are widely used in orthodontics and related disciplines and help to provide improved understanding of how a patient's teeth and bite function. The study of the static relationship of teeth and bite that is provided serves a number of functions, including a diagnostic function for interpretation of discrepancies or problems related to the bite relationship. The study casts further improve communication as a concrete model, helping the practitioner and patient to better understand discrepancies in tooth function. The dental study cast also helps to more precisely define pre-existing static bite relationships prior to the performance of any corrective work.
The plaster cast is formed using a series of impressions taken to obtain the geometry of the teeth. To take an impression, alginate or other impression material is poured into a tray (i.e., an impression tray) which is then introduced into the patient's mouth for a period of time (typically one to two minutes). The impression material sets about the teeth and soft tissues forming a negative impression. The patient also bites into a soft material for registering a simultaneous imprint of the upper and lower teeth which records the relationship of the teeth in the upper and lower jaws respectively in three planes of space. Once the impressions have set, they are sent to a lab to be processed into an upper and/or lower plaster study cast. The study casts are articulated together via the bite registration material to reproduce the bite of the patient. After construction, the study casts are returned to the dentist/orthodontist as a working study cast.
One aspect of conventional preparation methods relates to the number of labor intensive steps to produce the study casts, the space and storage of the study casts, and the inability to interface the study casts interactively with other diagnosis information (e.g., photographs and radiographs). In some cases, if additional work is required, or if the cast fails in some way or is damaged or lost, an additional impression series is taken. Therefore, there also exists a need in the art to develop a set of electronic data from the series of dental impressions wherein only a single impression need be taken for multiple interactive functions.
In a conventional sequence for orthodontic planning, the cast that represents the patient's teeth can then be scanned, such as using laser scanning or using a computed tomography (CT) or a cone-beam computed tomography (CBCT) scanning apparatus. The scanned data then provides baseline information as a reference for subsequent adjustments to tooth positioning that will be made over time. The process for obtaining this data requires several of the same steps used for conventional cast preparation. First, a negative impression is made of the patient's teeth, such as impression formed using an alginate material and provided in a tray. Next, the impression is used as a mold for casting the positive mold or model of the patient's dentition. The positive mold is then scanned using laser scanning or CBCT to form a volume image. The volume image that is generated in this way can then be used on a 3-D visualization system for modeling adjustments to be made to tooth position and angle. General techniques for producing plaster casts of teeth and generating digital models using laser scanning techniques are described, for example, in U.S. Pat. No. 5,605,459 (Kuroda).
Among drawbacks of the conventional method is the formation of a plaster mold to serve as an intermediate for the CBCT scan. Preparing the mold is a labor-intensive manual process, takes time, and, even when performed by a skilled technician, can suffer from some inaccuracy and dimensional distortion. The plaster model that is made is fragile and subject to damage.
For conventional approaches to providing a model of teeth in the upper and/or lower jaw of a patient, reference is made to WO2009/042378 (Puffier) and to U.S. Pat. No. 8,573,972 (Matov). Reference is also made to U.S. Pat. No. 7,140,877 (Kaza) and U.S. Pat. No. 6,767,208 (Kaza). Scanning of the mouth or an impression using optical systems is described, for example, in U.S. Pat. No. 7,905,725 (Chisti). Scanning using a hand-held scanning device is described in U.S. Pat. No. 7,068,825 (Rubbert). Laser scanning is described in U.S. Pat. No. 6,217,334 (Hultgren). Reference is also made to EP 1119312(B1) (Jones), CA 2346256(A1) (Chishti), and U.S. Pat. No. 6,532,299 (Sachdeva).
While these disclosures may help to provide some level of volume imaging information from scans of the mouth or of dental impressions/plaster casts, there is still room for improvement.
There is a need for methods that simplify the generation and use of models of tooth surfaces for orthodontic planning.